This invention relates to packet data services in telecommunications systems, and, more particularly, to control structures for contention-based packet data services in cellular telecommunications systems.
Major cellular system types include those operating according to the Global Services for Mobile (GSM) Standard, the TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual Mode Wide Band Spread Spectrum Cellular System (IS-95A), the TIA/EIA/IS-136 Mobile Station-Base Station Compatibility Standard (IS-136), and the TIA/EIA 553 Analog Standard (AMPS/TACS). Other major cellular systems include those operating in the personal communications system (PCS) band according to the IS-95 based ANSI-J-STD-008 1.8-2.0 GHz standard or those operating according to the GSM based PCS1900 (1900 MHz frequency range) standard. IS-95A is currently being updated, as IS-95B, in the document TIA/EIA SP-3693.
Currently, each of the major cellular system standards bodies is implementing data services into its digital cellular specifications. A packet data service specification has been finalized for GSM and IS-95A. Packet data service specifications compatible with the IS-136 and IS-95B standards are also being prepared.
In IS-95A the packet data service (IS-707) is implemented on a single channel, which is used on a make and break basis for multiple connections over the duration of a packet data session. Once a channel is seized, it is held by a call until it is timed out. The IS-707 scheme is inefficient and does not allow efficient utilization of channels by multiple packet data users. In the IS-95B packet data service (IS-707A), a fundamental channel is assigned and held similarly to the IS-95A fundamental channel, but a packet data call may also be assigned one or more supplemental channels, as necessary and as available, by a call control function. The supplemental channel packet function is handled by the Medium Access Control (MAC) function of the base station (BS). The packet data service is similar to true contention-based MAC principles as far as the handling of the supplemental channels. Supplemental channels are allocated among various users by the MAC function according to the relative fill levels of buffers set up for each call. Because the fundamental channel provides chip level synchronization information for the supplemental channels, physical layer access delays to supplemental channels may actually be reduced as compared to contention-based access schemes. The BS monitors all packet users buffers regularly and allows the supplemental channels to be shared by the users in a round-robin fashion. On the reverse link, the BS monitors requests from all the mobiles using the packet data service and allocates or de-allocates the supplemental channels accordingly.
A problem with IS-707 and IS-707A-based packet data services lies in the inefficiency caused by use of the fundamental channel. Assigning a fundamental channel to each packet call automatically takes 9.6 kbps of resources from the total resources available. Each user assigned a fundamental channel requires dedicated BS hardware resources until the fundamental channel is timed out. If the time-out period is shortened, this may cause a load in terms of network signaling and circuit switching. Overall, this scheme may lead to excessive packet delay due to call setup delays or excessive blocking as load increases and fundamental channels become the dominant portion of total resource consumption. At the point where excessive blocking occurs, a true contention-based system would allow more effective sharing of limited resources.
It is an object and advantage of this invention to provide an efficient method and system for transmitting packet data over a cellular telecommunications network that overcomes the foregoing and other problems.
Another object and advantage of this invention is to provide a method and system for handling multiple access of packet data users over dedicated traffic channels in a manner that reduces the system overhead required to support multiple users and reduces access delay of a packet user in obtaining use of a channel.
A further object and advantage of this invention is to provide a method and system for handling multiple access of packet data users in a manner that allows packet users having packet switched data, and/or packet users having simultaneous circuit switched (voice calls) and packet switched data to be handled under the control of a single control structure.
A method and system for transmitting packet data over a cellular telecommunications network is presented. A novel medium access control (MAC) logical layer is implemented between a service option layer and multiplex sublayer. The MAC layer handles the multiple accesses of packet users over selected dedicated traffic channels. The MAC layer provides a multiple access control function for packet data users only. Users requiring only circuit switched services (voice calls) are not serviced through the MAC layer multiple access control function. If a user has simultaneous circuit switched and packet data services operating, the MAC layer multiple access control function handles the packet data services, while the circuit switched services are handled simultaneously by bypassing the MAC layer multiple access control function.
In an embodiment of the invention, the MAC layer is implemented in a cellular telecommunications system utilizing a fundamental channel and/or one or more supplemental channels for each of the mobile-to-base station (reverse) and base-to-mobile station (forward) links. The MAC layer defines the radio resource request/management (data rate control) functionality in the mobile station and base station for efficient packet transmission. For users who already have a physical circuit with the network, e.g., those users already having a fundamental channel for voice but needing additional traffic resources for packet data, MAC is responsible for allocating additional supplemental channels as necessary or data rate requests/assignments for the purpose of transporting large packets. For users who do not already have a physical circuit with the network, the MAC layer is responsible for establishing a MAC layer connection between the mobile station and base station and allocating the physical layer connections on both the fundamental and supplemental channels.
The MAC layer multiple access control function interfaces between the service option layer and the system multiplex layer, i.e., TCP/IP packets arriving from a network layer are handled by the service option layer where they are encapsulated into point-to-point protocol (PPP) packets and passed to the MAC layer. As an alternative, the function of encapsulating the packets into RLP frames may be performed in the service option layer before the packets are passed to the MAC layer. The MAC layer processes the packets into radio link protocol (RLP) frames and provides a MAC layer multiple access control function that processes the data and passes the data to the system multiplex layer. The system multiplex layer handles the system specified, multiplexing and formatting for transmission on the traffic channels of physical air interface. Circuit switched service options interface to the system multiplex layer without handling through the multiple access control function layer of the MAC. The interface for the circuit switched service options may be directly to the multiplex layer or be through the MAC layer but not through the multiple access control function of the MAC layer. The multiplex layer may be implemented under one common control function or, as an alternative, may be split into two separately functioning layers, with one handling circuit switched service options and the other handling packet data service options.